Summary

The exploration of magnetic structures at an ever smaller -- ultimately atomic
-- scale is currently a topic of great scientific interest. It is also of highest
technological relevance in engineering extreme density magnetic data storage devices and developing the new field of magneto-electronics. In this
present work spin polarized scanning tunneling spectroscopy (SP-STS) is introduced as a new, extremely versatile investigation tool. For the first time,
its application on a routine basis is comprehensively demonstrated. Regarding spatial resolution, this method surpasses other high resolution magnetic
microscopy techniques by two orders of magnitude.
After a general introduction given in Chapter 1 the theoretical foundations of SP-STM will be presented in Chapter 2. The instrumental setup of a
scanning tunneling microscope, custom designed for the purpose of magnetic
investigations, is described in Chapter 3. First results in the study of the
microscope's magnetic sensitivity were obtained on thick (50 monolayers)
and thin (7 monolayers) Gd films grown epitaxially on W(110). These measurements also provided important insights into the magnetic anisotropies
of tunneling tips coated by ferromagnetic thin films and will be discussed in
Chapter 4. As an introduction to the investigation of the system of nano-
scale iron wires grown on a stepped W(110) substrate an overview of previously published results will be given in Chapter 5. Arrays of Fe nanowires
will then be used in Chapter 6 as a model to discuss the practical application
and the magnetic contrast mechanism of the microscope. Optimized for highest spatial resolution, the method will then be applied to a detailed study of
the magnetic domain structure of the Fe stripes which are characterized at
the nanometer scale by a complicated interplay of competing anisotropies.
In Chapter 7 observations of stripes of single atomic layer thickness and
stripes of two layers thickness are described, the magnetization being in the
film plane for the former, and perpendicular to the film plane for the latter.
Chapter 8 is dedicated to observations made on the array of Fe stripes in
variable external magnetic fields. A complete hysteresis loop is presented,
acquired at the nano-scale. Also, details of the remagnetization process like
domain wall motion, domain creation and annihilation, are observed. These
results highlight the important fact that SP-STS can routinely be applied in
strong magnetic fields.